1. Field of the Invention
This invention relates to a magneto-optical recording method of recording information on a magneto-optical recording medium.
2. Related Background Art
The information overwriting method using a magneto-optical recording medium is broadly divided into the light modulation system and the magnetic field modulation system. The light modulation system includes the light modulation overwrite system utilizing the difference in thermal magnetic characteristics between two layers of a magnetic film, i.e., a recording layer and an auxiliary layer, as described, for example, in Japanese Patent Application Laid-Open No. 62-175948.
On the other hand, the magnetic field modulation system is a system as described, for example, in Japanese Patent Application Laid-Open No. 57-186248 wherein a light beam is applied a to magneto-optical recording film and at the same time, an extraneous magnetic field modulated in conformity with a recording signal is applied to the region of the film to which the light beam is applied, whereby the direction of magnetization is changed in conformity with recording information to thereby accomplish the recording of information.
However, in the overwriting system using two layers of magnetic film and the light modulation overwriting system utilizing an anti-magnetic field, when the recording domain length becomes short as indicated by a solid curve in FIG. 1 of the accompanying drawings, the carrier level corresponding to the amplitude of a reproduction signal is greatly reduced. FIG. 2 of the accompanying drawings shows the relation between the temperature distribution of a recording layer by the application of light and the recorded domain. When the laser recording wavelength is 780 nm and the N.A. (Numeral Aperture) of an objective lens is 0.53, the laser beam diameter is approximately 1.4 .mu.m. Also, this is an example in which the recording land width is 1.0 .mu.m and the domain was formed at a duty of 50%. In the light modulation recording system, when laser light is applied, the temperature distribution of the magneto-optical recording layer becomes a substantially Gaussian distribution and domains are formed in areas wherein the temperature is about T.sub.C or higher. Accordingly, the recording domain length and the recording domain width were made substantially the same. FIG. 2(a) shows an example in which the recording domain length is 0.8 .mu.m, FIG. 2(b) shows an example in which the recording domain length is 0.6 .mu.m, and FIG. 2(c) shows an example in which the recording domain length is 0.5 .mu.m. There has been the problem that when the recording domain length decreases thusly, the carrier level is greatly reduced as already noted.
On the other hand, the magnetic modulation system is a system as shown in FIG. 3(b) of the accompanying drawings wherein upward and downward modulation extraneous magnetic fields are applied to a magneto-optical recording layer to thereby change the direction of magnetization to upward and downward directions. Accordingly, domains formed are of a substantially constant domain width, irrespective of the magnitude of the recording domain length, as shown in FIG. 3(a) of the accompanying drawings. Consequently, as indicated by a dotted curve in FIG. 1, the reduction in the carrier level caused by a decrease in the recording domain length becomes smaller than in the light modulation recording method.
However, in the magnetic field modulation system, the recording speed is limited by the magnetic field modulation speed and therefore, high-speed recording has been difficult. Not only has there been the possibility of crushing of a floating magnetic head or the like, but also the need for additional devices such as a magnetic head and a driver therefor has been increased, and this has led to the problem that the apparatus becomes complicated and bulky.